We have been studying quantitative neuronal density, neuronal size and nuclear size in selected areas of brains from patients with certain neuropsychiatric disorders as well as normal controls from different age groups. Results to date indicate that there is normally an age-related purkinje cell loss in the anterior vermis, posterior vermis and hemispheres of the cerebellum. In contrast, multipolar cells in the cerebellar dentate nucleus and hipocampal pyramidal cells (with a possible exception of those in the sector CA4) show no significant change with aging. The reasons for such differential vulnerability of neurons to aging are still unclear, but probably include differences in catecholamine content. We found no significant differences in any of the measures related to cerebellar Purkinje cells, between controls and patients with major psychiatric disorders including schizophrenia, unipolar and bipolar disorders. There was, however, a suggestion for a decrease in Purkinje cell density related to long-term treatment with neuroleptics.